Page 268 - Biaxial Multiaxial Fatigue and Fracture

252 M. END0

cycles for a fixed value of do. The minimum increment in stress level in determining the
fatigue limit was 5 MPa for greater value of o and r, except for Cr-Mo steels where 10 MPa
was used.

RESULTS AND DISCUSSION

Behavior of small cracks at the threshold level

Figures 7 and 8 show the non-propagating cracks emanating from a hole at the fatigue limit of
hole-containing Cr-Mo steel and brass specimens. As seen in these figures, the direction of non-

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50 pm

(a) Tension-compression; ow = 340 MPa.

1
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Axial direction
50 pm

(b) Combined loading; oa = ra = 200 MPa.

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Axial direction
50 pm

(c) Pure torsion; rw = 320 MPa
Fig. 7. Small non-propagating cracks emanating from hole at fatigue limit of
quenchedtempered SCM435 steel; & 83 pm (d = 90 pm).
=